Air-conditioning systems for public transportation vehicles pose special design problems and challenges. Such a system must be capable of offsetting to an established degree the relatively high heat load expected to be generated by the maximum density of passengers for which the vehicle is designed. Conditioned air must therefore be delivered to the passenger cabin at a relatively high cooling rate. For example, with respect to a railcar of approximately 5400 cubic feet, typical cooling specifications require conditioned air to be delivered at the rate of about 3600 cubic feet per minute (C.F.M) which is equal to a complete air change within the vehicle every 1.5 minutes (approximately five times the rate of a normal residential cooling system).
At such delivery rates, significant problems occur with respect passenger comfort. Precise control over the direction of air flow within the vehicle cabin, and in particular with respect to the air flow in the vicinity of the diffuser outlet must be exercised. Since circulating velocities within the vehicle must be relatively high, impingement of the circulating air upon the passengers (particularly those located in proximity to the diffuser outlet) must be avoided in order to preserve their comfort.
Heretofore, vehicle air-conditioning systems have employed a plurality of interconnected air-diffusing outlets distributed throughout the vehicle passenger cabin at predetermined locations. Unfortunately, such prior arrangements have been found to result in undesirable drafts on passengers situated in the vicinity of the outlets, particularly with respect to standing passengers.
One technique which has been utilized heretofore for lowering the velocities at which conditioned air exits from the diffusing outlet (without affecting the cooling rate) is to provide a linear diffuser element which extends continuously along the full length of the vehicle from one end to the other. It is well understood that such a diffuser delivers air at exit velocities which (for a given cooling rate) are less than those which would be present at each of a group of dispersed diffuser outlets as described above.
However, even the use of linear air diffusers has generally failed heretofore to satisfy several basic requirements for adequate passenger comfort. These requirements are essentially as follows:
(1) the rate at which the linear diffuser delivers conditioned air to the vehicle cabin must be substantially uniform throughout the length of the diffuser;
(2) the direction in which conditioned air exits from the diffuser outlets must be carefully controlled to avoid its being dumped onto the passengers; and
(3) conditioned air delivered by the air-conditioning system must be adapted to mix thoroughly with ambient air of a different temperature within the vehicle.
An air conditioning system for public vehicles which satisfies all of these basic requirements has not been available heretofore. While it has been possible to achieve generally uniform delivery rates, none of the prior systems has been able to avoid to any significant extent, impingement of the conditioned air directly upon the passengers, particularly the standing passengers and those located proximate to the air delivery outlets.
These and other disadvantages of the prior types of air diffusers are obviated by the present invention in which the diffuser or air delivery nozzle is adapted to effect selected turbulence characteristics in the delivered air such that it tends principally to flow laterally outwardly along the ceiling plane of the vehicle toward the side walls of the cabin. The delivered air is thereafter turned downward by the cabin walls and circulates generally along the cabin periphery. The ambient air within the cabin is drawn into the circulating temperature-controlled air and is mixed therewith to effect comprehensive cooling of the cabin. The stream of conditioned air creates a shear effect as it passes over the inner surfaces of the vehicle ceiling and walls thereby to generate an additional degree of turbulence which facilitates the mixing.
In accordance with the invention, the output nozzle of the present diffuser is adapted to generate a cyclical or whirling turbulence within the delivered air flow. Such eddy current turbulence not only assists in mixing the ambient and delivered air, but causes the delivered air to hang near the ceiling as it moves outwardly toward the cabin walls rather than to drop onto nearby passengers. As a result, efficient cooling of the cabin is achieved without generating uncomfortable drafts on the passengers.
These and other objectives of the present invention are obtained by providing a linear air diffuser which extends longitudinally along the length of the passenger vehicle at its ceiling. In one embodiment of the invention, the diffuser nozzle includes a pair of outwardly diverging longitudinal output channels defined in part by the sidewalls of a central rail or vane of generally Y-shaped cross-sectional configuration. The sidewalls are shaped into a pair of back-to-back generally concave external surfaces each of which forms one interior wall of each of the output channels. A pair of substantially U-shaped longitudinal side rail members coextensive with the central rail are connected to opposite sides thereof in spaced relation to the concave surfaces and open laterally outwardly in opposite directions. The inwardly facing continuous surface areas of the base section and laterally extending lower flange of each of the side rails forms the other interior wall of each of the output channels. Each of the lower flanges may be provided with a generally planar section which is parallel to and overlies for a predetermined distance the opposite interior wall of the channel near the output opening. Air entering the two channels at their inner ends is deflected to flow laterally outwardly away from the diffusor in substantially opposite directions.
Entrance of pressurized air to the two channels at their respective inner ends is controlled by each of a pair of generally parallel orifice slots or openings which extend longitudinally along the length of the diffuser. In one embodiment, the orifice openings are defined on one side by the longitudinal peripheral edges of a substantially flat orifice plate centered at the top of the central rail and coextensive therewith. The other side of each of the orifice openings is determined by an opposing peripheral edge formed along each of the side rails.
In accordance with the invention, the size of the orifice openings may be fixed, by adjusting the plate width in relationship to the static pressure of conditioned air available within the system upstream of the output nozzle. In this way, a desired delivery rate for the diffuser (determined by the orifice opening) may be achieved for a given air supply pressure, such that the delivery rate remains consistent throughout the vehicle length.